Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Engine suddenly running terrible

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ourkid2000:
Morning folks, I could use some advice. My 66' Toronado was running awesome until yesterday and I'm kinda lost trying to figure out where to start.

Quick backstory: I got my rebuilt QJet back from the rebuilders a couple weeks ago and I installed it on the car with no problems and, I have to say, it has never run better after putting that carb on. Quick start ups, the throttle felt snappy and smooth, and the choke was working perfect, pulling off almost exactly on the money......great right? Well a couple days ago I started up the car in my garage just to give it a quick run (not out for a drive, just a quick garage start-up) and, again, it ran perfectly. Smooth, snappy, etc. I shut er down after about 5 mins and that was that.

Fast fwd to the next day and I had just received a replacement vacuum driven headlight actuator which I was going to throw in and see how the headlights performed. I installed it, but accidentally left one of the vacuum lines off (the little actuator on top that releases) and when I started the car it kinda revved a bit too high and when I kicked off the fast idle it started to fall on its face. I realized I had left a vacuum line off and I reattached it. Since all this happened, the car has run like absolute dog s***. Perhaps all that is unrelated and something else has happened, I don't know.

Anyway, the car starts up alright but it's wanting to die all the time. You give it gas and it stumbles like crazy and it kinda reminds me of my old snowmobile when it would run on one cylinder rather than two,.....just seems lifeless or something. It sounds off, not smooth like before. I did notice when I pulled the choke over to the near-closed position that it smoothed out a bit and revved up.

So, what have I tried so far? I wanted to rule out fuel delivery to the carb so I watched for the squirts of fuel from the accelerator pump. Two strong streams of fuel coming out so that's good. I also hooked up a fuel pressure test rig and started the car. The PSI ranged from 7-9 roughly depending on throttle position, so that's not ideal but ok I think. I also capped off the vacuum port that feeds the headlights and HVAC system, just to rule out any vacuum leaks in that system. Still the same result.

Anyway, I'm pretty new to this and am learning as I go. I was going to have a look at the ignition next......just to check the timing, clean the points, swap in a replacement condenser. I actually had replaced the points and condenser about a month ago and it was running great since then. Maybe something going on there? God, I dunno guys....I'm pretty lost. I really don't want to crack into my freshly rebuild carb!

Mudsport96:
Well, since all of this started AFTER the headlight actuator install. I would unplug it and cap off the vacuum line going to it. Then start the car and see if there is a difference. Everything you described tells me the air/fuel mixture is wrong. Especially the part about closing the choke stabilizing the idle but making rpm increase. You are reducing airflow at the carb and adding fuel... so somewhere you have enough air coming in to burn the extra fuel. And what was the last modification done? Vacuum actuator for the lights.

ourkid2000:
Yeah, I did mention that I capped off the line that feeds the headlights vacuum and the HVAC system to rule out anything there. After I capped the manifold fitting it still ran the same. I've double checked the rest of the vacuum lines and I don't see anything off.

Yeah the last thing I did was replace the headlight actuator on the drivers side. The day before I was running the car and it ran absolutely tip top.

Cliff Ruggles:
The symptoms sound like a vacuum leak someplace.  I would investigate further.  Might want to remove the carb and check the gasket(s) under it.  Not sure if your set-up uses exhaust gas to heat the carb but if it does it may have developed a leak there.......

ourkid2000:
So this randomly resolved itself, it seems.

What did I mess with? Well, the only thing I played with was the PCV hose to hook up my vacuum gauge. I reconnected the PCV hose and it seems to be running tip top again.

Cliff, is it possible for the carb gasket to have an intermittent vacuum leak? I would guess not but you never know?

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